Summary On 02 October 2006 during twilight at 0615 eastern daylight time, shortly after having cleared the exit of the lock, the downbound tug PetiteForte, pushing the barge St.MarysCement, drifted backwards and struck the arrester cable in Lock4 of the Welland Canal. The tug's mast and electronic navigation equipment were damaged. The shear pins and linkage for the lock's ship-arrester cable needed to be replaced. Ce rapport est galement disponible en franais. Other Factual Information Particulars of Vessels Tug and Barge Description The tug PetiteForte has an upper and lower wheelhouse. The upper wheelhouse is used more often for navigation when pushing the barge St.MarysCement, especially when in ballast as it provides better visibility than is possible from the lower wheelhouse. In pushing mode, the PetiteForte has 38percent of its length positioned in the notch of the barge. The tug is connected to the barge by two steel cables so as to prevent tug movement astern. Lateral motion is restricted by side pads with zero clearance between the tug and barge. This renders both vessels a single composite unit approximately 134m in length (see Photo1 and Photo2). Crewing Requirements The PetiteForte's upper wheelhouse comfortably accommodates one person for navigation purposes but not two. In recognition of this fact, The St. Lawrence Seaway Corporation allows the vessel to meet crewing requirements by allowing one qualified person in each of the upper and lower wheelhouses when the vessel is underway within the confines of the St. Lawrence Seaway.2 In this occurrence, the officer of the watch (OOW) was stationed in the communications area in the forward part of the lower wheelhouse. Description of Lock 4 and Adjacent Area Locks 4, 5, and 6 in the Welland Canal section of the St. Lawrence Seaway are dual capability locks that allow vessels to transit simultaneously both upbound and downbound. The last downbound lock of this group is Lock4. When approaching Lock4 from Lock3 (upbound), there is the possibility of hydrodynamic interaction between vessels as the canal narrows towards Lock4. To prevent this, a 100m "bullnose" has been constructed. This is a concrete pier that protrudes from the locks (see Figure1). A few metres past the Lock4 gates (when moving downbound towards Lock3), but well before the tip of the bullnose, lies Canadian National (CN) Rail Bridge No.6. This is a moveable "Bascule" bridge that can be opened or closed to allow vessels to pass. History of the Voyage On 01 October 2006, the tug PetiteForte, pushing the barge St.MarysCement in composite unit, was downbound in Lake Erie en route from Toledo, Ohio, to Bowmanville, Ontario. At 23003, the unit proceeded from Long Point towards Port Colborne and into Lock8 of the Welland Canal. The master was alone in the tug's upper wheelhouse. The OOW was stationed in the communications area in the forward part of the lower wheelhouse. At 0538, after passing through Locks7, 6, and5, the composite unit entered and was secured in the east chamber of Lock4. At 0549, the composite unit was lowered within the lock and at 0600 it was ready to leave the lock. At this point, only its mast showed above the lock's wall. At 0602, the ship traffic controller, who was concluding his shift, used a very high frequency (VHF) radiotelephone to instruct the PetiteForte to move to the head of the lock area and, once there, to maintain position until the bulk carrier Algomarine, upbound from Lock3, began entering the west chamber of Lock4. The ship traffic controller was then relieved by the controller for the next shift. The two exchanged situational information until approximately0605. At 0609, the stern of the tug cleared the Lock4 gates. A Lock4 lines person then signalled the lockmaster that the stern of the PetiteForte had cleared both the lock gates and CN Rail Bridge No.6. Procedures were then initiated to turn back the lock in preparation for the next downbound vessel (see the section titled Lock 4- Normal Operating Procedures). At 0611, the ship-arrester cable was lowered across the east chamber's lock entrance, astern of the PetiteForte. In keeping with normal practice, there was no VHF communication with the PetiteForte by either the Lock4 lock operator4 or Seaway traffic control to say that the arrester cable had been lowered (see Photo5), nor was such communication required. At this time the composite unit was at the head of the lock area with the tug's stern approximately 10m beyond the Lock4 gates. In accordance with lock procedures, the Lock4 Seaway personnel stopped spotting the tug and shifted their attention to the west side (upbound) section of the lock in preparation for the Algomarine's arrival. While the composite unit was holding its position at the head of the lock, the Algomarine's approach created a surge of water that raised the water level by 5cm. The force of this surge pushed the composite unit astern, towards the chamber it had just left. At 0612, the new ship traffic controller could see on a monitor that the composite unit was drifting astern into the lock. The controller informed the PetiteForte via VHF radiotelephone that it had been instructed to hold position inside the east chamber until the Algomarine entered the west chamber, along with a reminder that the tug was to do this in the future. Although this contradicted the original instruction to proceed to the head of the lock area and hold position, the master neither questioned nor challenged the new ship traffic controller's comment. He did not ask for clarification. Instead, the master interpreted the comment as a change of instructions. He was thus unconcerned when the composite unit began to drift astern, back into the lock. At 0613, the master indicated to Seaway traffic control that he was stopping his vessel and would wait for the Algomarine to arrive in the west chamber of Lock4. A Seaway traffic control video playback shows that the tug continued to move astern. At 0615, while drifting astern with the water surge, the tug's mast struck the ship-arrester cable. The impact buckled the mast and disabled most of the electronic navigation and communication equipment. The arrester cable's connecting link attachments, as well as the mechanical/spring buffer system, were also damaged. After an initial damage survey and inspection by Seaway and Transport Canada inspectors, the tug was cleared for transit to Wharf1 for repairs. Head of the Lock Terminology Whenever another large vessel, such as a bulk carrier, approaches upbound towards Lock4, Seaway traffic control instructs any vessel departing Lock4 downbound not to proceed much beyond the head of the lock area and, once there, to hold its position. The term, although not specifically defined, applies to an approximate area from the lock chamber gates up to and including the tip of the bullnose, but not usually beyond the pointL/A2 (Limit of Approach2), which is approximately 25to 30m beyond the bullnose (see Figure1). In practice and for the Lock4 area, the term is generally taken to mean that a vessel's bow be positioned outside of the open lock gate doors and near or slightly forward of the tip of the bullnose. The position for the head of the lock will change from lock to lock according to lock construction variations and Seaway traffic control instructions. Depending on overall length, it is also possible for a vessel to be located at the head of the lock and yet remain partially within the lock chamber. In this occurrence, the stern of the PetiteForte was approximately 10m beyond the lock gates, the majority of its length was back of the bullnose, and its bow was some distance beyond the tip- possibly slightly pastL/A2. Such a position would be considered within the head of the lock area for this lock. Lock 4- Normal Operating Procedures When the water in the east chamber reaches its maximum level, the lock is considered filled. Before a downbound vessel enters, the forward arrester cable is lowered and locked in place, transversely across the lock, so as to prevent the vessel's bow from striking the forward lock gate. After linespersons secure the vessel, the rear ship-arrester cable is lowered into place behind the vessel. The water in the chamber is then released5 and the vessel is lowered (approximately 13m in the case of Lock4). At this point the gates are opened, the forward arrester cable is raised, the vessel's mooring lines are let go, and the vessel begins moving ahead towards the lock exit according to any instructions given by Seaway traffic control. If there is no upbound vessel approaching from Lock3, the downbound vessel can proceed without restriction. If there is, however, then the downbound vessel will be instructed by Seaway traffic control to hold position at the head of the lock.6 The purpose of waiting in this area is so that the downbound vessel will still have the protection of the bullnose "buffer" and thus avoid the possibility of hydrodynamic interaction that could otherwise take place with two large vessels transiting in opposite directions in such an enclosed space. The bullnose also protects against the water surge created by an upbound vessel which can cause a downbound stationary vessel to drift astern.7 Typically, a downbound vessel waiting at the head of the lock will remain there until the majority of the oncoming upbound vessel's length has passed into the opposite chamber. Once the downbound vessel fully clears the lock chamber, the arrester cable is lowered again (for the next vessel) and the lock gates are closed. Neither Seaway traffic control nor the lock operators inform a departing vessel that these lock preparation procedures have begun. Seaway personnel also stop spotting a vessel at this point, shifting their attention to any vessel approaching the upbound section of the lock. Weather The area weather recorded by Environment Canada for 02October2006, at 0600, indicated clear visibility under cloud cover and light winds from the south-southwest at six knots. Personnel Certification The master had a Foreign-Going Master's certificate and had been working with this company for 10years, the last seven as master. He averaged 40to 45trips through the Welland Canal per year and he was well-versed with canal operations. Communications The Seaway traffic control centre communicates with shipping traffic on VHF channel14, in addition to monitoring channel16. The Seaway traffic control centre for this section of the seaway is located near Locks4, 5,and6.8 The lockmaster at Lock4 communicates with vessels separately on channel66A and channel17 for Lock4 east and west, respectively. Communications on these latter two channels are generally not monitored by Seaway traffic control. Lock personnel use a conventional "land line" to communicate with Seaway traffic control. At the time of the occurrence, neither Seaway traffic control nor Lock4 VHF communication channels were used- nor were they required to be used- to inform the master of the PetiteForte that the ship arrester had been lowered. Damage to Vessel The PetiteForte suffered damage to its main mast, which was sheared-off at the deck. All the electronic navigation and communication equipment was rendered non-operational including the following: radars, DGPS unit, navigational lights, anchor release antennae, and radio antennae (see Photo6). Damage to the Arrester Cable The shear pins and linkage for Lock4's arrester cable were broken.9